A hybrid powertrain typically includes an engine and one or more motor/generators that cooperate to efficiently supply power to propel a vehicle. Some vehicles with hybrid powertrains are able to turn off the engine and rely on torque supplied solely from at least one of the motor/generators in certain operating modes to improve fuel economy; when operating conditions require positive engine torque, the engine is restarted using torque from one of the motor/generators in what is referred to as an “autostart.” In some hybrid powertrains, the motor/generators are part of the transmission, and torque from the motor/generators to restart the engine is transmitted to the engine crankshaft via the input shaft of the transmission.
A damper is often used in the connection between the engine and the transmission input shaft to reduce vibration and filter out high-frequency engine torque oscillations while transferring engine torque. The damper is desirable when torque is being transmitted from the engine to the transmission, but the damper is not desirable when torque is being transmitted from the transmission or the motor/generator to the engine during an autostart.
Some hybrid powertrains utilize a damper bypass clutch (DBC), which is engaged during an engine autostart in order to bypass the damper. When engaged, the DBC provides a separate, undamped connection between input shaft and the crankshaft. The DBC is released during normal operation, restoring the damper function. The DBC is typically hydraulically actuated, and controlled by a powertrain controller. The powertrain controller engages the DBC in anticipation of an autostart event.